Here are the fuel pressure requirements for a 1st Generation Dodge Cummins with a Bosch VE injection pump.
Maximum Inlet restriction ............................... 4 In Hg
Maximum Return line Restriction ................ 20.4 In Hg
Maximum pressure drop across fuel filter ............ 5 PSI
Maximum pressure at the injection pump .......... 10 PSI
Minimum pressure at the injection pump ............. 3 PSI
Volume of fuel pumped in 30 seconds ........ 0.79 Quarts
The maximum inlet and return line restriction is measured using a vacuum pump against the lines looking for flow restrictions. Minimum and maximum fuel pressure are measured between both idle and WOT operation looking for the performance of the fuel pump are with the specification. The measured fuel pressure should be measured near the injection pump. The volume of fuel is measured by disconnection the fuel line and disconnecting the fuel shutoff solenoid and cranking the engine for 30 seconds.
WARNING! Don't crank the engine for more than 30 seconds or starter damage could occur. If you need to repeat the test allow the starter to cool for at least 2-3 minutes before testing again.